<-[[.:start]] ====== R Pi Image files ====== ===== Various tips and tricks for working with Raspberry Pi Disk Images ===== ==== Taking an image ==== - remove SD card from Pi - insert into PC - unmount the image partitions if they get auto-mounted - take the image using ''dd''sudo dd if=/dev/mmblahblah of=name_of_image.img bs=4M - wait..... and wait.... - this can now be either - saved as it is (possibly a big file) - compressed with gzip gzip name_of_image.img - an alternative is to make sure the image is as small as it needs to be, appropriate to the space actually needed by the installed OS. ==== Using ''losetup'' to work with the image file ==== The image can be used as a //loop// device and then mounted as a normal disk to allow access to the files etc. To access the image as a //loop// device you let ''losetup'' find the partitions automatically and convert them to to loop partitions ''loop0p1'' (the ''/boot'' partition) and ''loop0p2'' the ''root'' partition. You can then mount whichever one you need. gm4slv@laptop:~/piimg $ sudo losetup -Pf igate.img gm4slv@laptop:~/piimg $ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT loop0 7:0 0 4.3G 0 loop ├─loop0p1 259:0 0 256M 0 part └─loop0p2 259:1 0 4G 0 part sda 8:0 0 298.1G 0 disk ├─sda1 8:1 0 235.1G 0 part / ├─sda2 8:2 0 1K 0 part ├─sda3 8:3 0 50.9G 0 part └─sda5 8:5 0 12.1G 0 part [SWAP] sr0 11:0 1 1024M 0 rom gm4slv@laptop:~/piimg $ sudo mount /dev/loop0p2 /mnt gm4slv@laptop:~/piimg $ cd /mnt gm4slv@laptop:/mnt $ ls bin boot dev etc home lib lost+found media mnt opt proc root run sbin share srv sys tmp usr var gm4slv@laptop:/mnt $ cd etc/ gm4slv@laptop:/mnt/etc $ cat hostname igate gm4slv@laptop:/mnt/etc $ This allows you to change files (one example is to set a fixed IP address in ''/etc/dhcpcd.conf'') as required. ==== Shrinking the image ==== If the OS had been expanded after install to //fill the whole SD Card space// there is now a lot of pointless wasted space in the image that - takes up disk space to store - makes copying to a new SD card slow - makes it impossible to copy to a smaller card The image can be shrunk to a more appropriate size. The gist of it is [[https://superuser.com/questions/610819/how-to-resize-img-file-created-with-dd|here]] * unmount the loop device: sudo umount /mnt * use ''gparted'' (need to be at a machine with a graphical session) to shrink the partition to a more suitable size, leaving some room for safety * dispose of the ''loop'' device sudo losetup -d loop0 * The *.img file is still the same size, but the partitions within the file are smaller, the rest of the space needs to be stripped from the *.img file with ''truncate'' * Use ''fdisk'' to inspect the image file to see where the partitions start and end * gm4slv@laptop:~/piimg $ sudo fdisk -l igate.img Disk igate.img: 4.25 GiB, 4563402752 bytes, 8912896 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x38ea48c4 Device Boot Start End Sectors Size Id Type igate.img1 8192 532479 524288 256M c W95 FAT32 (LBA) igate.img2 532480 8912895 8380416 4G 83 Linux * The second partition ends at block **8912895** so you shrink the filesystem to this point (plus one). This requires the calculation of the actual number of bytes, based on the **block size of 512 bytes**. * Either calculate it yourself, or put the calculation in the command: * sudo truncate --size=$[(8912895+1)*512] name_of_image.img Voila, a smaller image on file which uses //just enough// space for the //already known to be working// OS Page Updated: ~~LASTMOD~~ {{tag>linux pi}}